FIG. 1 is a structural diagram illustrating a conventional polycrystalline silicon resistance element and, in particular, a high resistance element which is formed on a semiconductor substrate. A polycrystalline silicon 2 is formed on semiconductor substrate 3 through insulating or oxide film 9 and is connected to aluminum electrodes 4 and 6 through contacts 5 and 7. Insulating film 10 is formed over the top surface of polycrystalline silicon 2 which overlays only aluminum signal lines or an oxide protective film.
FIG. 2 is a structural diagram illustrating a conventional resistance element 12 is formed on semiconductor substrate 13 using a low concentration diffusion or an ion implanted diffusion. Diffused resistor 12, formed on a surface of the semiconductor substrate 13, is connected to aluminum lines 14 and 16 through contacts 15 and 17. An insulating or oxide film 10 is formed over diffused resistor 12. The insulating film overlays only either other signal line of polycrystalline silicon or aluminum, or an oxide protective film.
However, in the case of the conventional structure shown in FIG. 2, a depletion layer occurs on the surface of resistance element 12 due to an electrical field from signal line passing to resistance element 12 and causes an increase in resistance value. In case where the depth of the depletion layer reaches to a degree that it is not able to be ignored with respect to the diffusion depth of resistance element 12, the resistance value greatly varies. An ion implanted resistance element with a depth of less than 1 .mu.m and a sheet resistance of 6 to 9 K.OMEGA. illustrates the phenomenon in a remarkable manner, and its resistance value may vary over several percent to several tens of percent.
Similarly, in case a high value resistance polycrystalline silicon 2 relative to FIG. 1, which is protected only by an oxide film 10, its resistance value is often varied due to impurity ions which permeate into the polycrystalline silicon.
A semiconductor element varies by nature its energy level in response to an incident light. Therefore, there has been a disadvantage that a resistance value is varied in response to light such as visible ray, infrared ray, or ultraviolet ray irradiated onto a semiconductor device.